US 20040146116 A1 Abstract A constant amplitude coded bi-orthogonal demodulator demodulates the received constant amplitude bi-orthogonal modulated data, cancels the parity bits to generate the serial data, detects the occurrence of an error by dividing the demodulated data into a plurality of groups of data, outputs the serial data as demodulated data if an error does not occur, sequentially converts bit polarities of data of groups in which an error occurs if the error detector detects the error, compares distances between the received bi-orthogonal modulated data and the constant amplitude coded bi-orthogonal modulated data, and selects, as demodulated data, data of which corresponding bit polarities are changed according to the comparison results.
According to the present invention, power consumption is reduced, a power amplifier can be manufactured at an inexpensive cost, interference robustness can be ensured, and data can be transmitted at a high transmission rate and a variable transmission rate.
Claims(8) 1. An apparatus for constant amplitude coded bi-orthogonal demodulation, comprising:
a bi-orthogonal demodulation unit for demodulating received constant amplitude bi-orthogonal modulated data, canceling parity bits and then generating serial data; an error detector for detecting the occurrence of an error while dividing the data demodulated in the bi-orthogonal demodulator into a plurality of groups of data and then outputting the serial data of the bi-orthogonal demodulator as demodulated data if an error does not occur; an error bit polarity converter for sequentially converting bit polarities of data of groups with errors if the error detector detects the errors and converting the data of groups with errors and the data of groups with no errors into the serial data; a constant amplitude coded bi-orthogonal modulator for performing the constant amplitude coded bi-orthogonal modulation for the output data of the error bit polarity converter; a distance comparator for comparing bit-by-bit distances between the received bi-orthogonal modulated data and the constant amplitude coded bi-orthogonal modulated data of the constant amplitude coded bi-orthogonal modulator; and a buffer for storing a number of serial data output from the error bit polarity converter and selectively outputting the corresponding serial data as demodulated data according to a control signal of the distance comparator. 2. The apparatus as claimed in a bi-orthogonal demodulator for demodulating the received bi-orthogonal modulated data; a parity bit canceller for canceling the parity bits from the output data of the bi-orthogonal demodulator; a plurality of switches for switching the data of the parity bit canceller according to the output signal of the error detector; and a parallel to serial converter for receiving the switched data from the plurality of switches if the error detector has not detected errors and converting the data into serial demodulated data. 3. The apparatus as claimed in first to third parity checkers for receiving the plurality of groups of data output from the bi-orthogonal demodulator, checking the parity bits, determining the occurrence of errors and controlling the plurality of switches; and an OR gate for generating an error determining signal by performing an OR operation for output signals of the first to third parity checkers. 4. The apparatus as claimed in first to third bit polarity converters for receiving the data of the groups in which errors have occurred through the plurality of switches and converting their polarities; a plurality of OR gates for performing OR operations for output data of the first to third bit polarity converters and data with no error switched in the plurality of switches; and a parallel to serial converter for converting output data of the plurality of OR gates into serial data. 5. The apparatus as claimed in a serial to parallel converter for converting the output data of the error bit polarity converter into a plurality of groups of data bits according to a data rate control signal; a constant amplitude encoder for generating the parity bits for the respective groups by combining the plurality of groups of data bits converted in the serial to parallel converter; an orthogonal code generator for generating a plurality of groups of orthogonal codes which are different from one another; a plurality of bi-orthogonal modulation units for selecting one orthogonal code in each of the plurality of groups of orthogonal codes according to the plurality of groups of data bits and the parity bits of the respective groups, managing the polarities and performing the bi-orthogonal modulation; and a parallel summer for parallel summing up output signals of the plurality of bi-orthogonal modulation units. 6. The apparatus as claimed in an orthogonal modulator for selecting as a polarity bit each one bit in each of the plurality of groups of data bits and a plurality of the parity bits for the respective groups and selecting one orthogonal code in each of the plurality of groups of orthogonal codes, corresponding to the remained bits except the selected one bit, and a multiplier for multiplying the output signal of the orthogonal modulator by the selected polarity bit to adjust its polarity and outputting the multiplied and adjusted signal to the parallel summer. 7. The apparatus as claimed in 8. The apparatus as claimed in _{0}), (r_{1}), (r_{2}) by logically combining the data bits (b_{0}˜b_{2}), (b_{3}˜b_{5}), (b_{6}˜b_{8}) of the respective groups according to the following formulas 2 to 4: r _{0} ={overscore (b _{0})}{circle over (+)}{overscore (b (2) _{3}+b_{6})}r _{1} =b _{1} {circle over (+)}b _{4} {circle over (+)}b _{7 } (3) r _{2} =b _{2} {circle over (+)}b _{5} {circle over (+)}b _{8 } (4) where {circle over (+)} represents XOR.
Description [0001] 1. Field of the Invention [0002] The present invention relates to an apparatus for constant amplitude coded bi-orthogonal modulation and demodulation, which modulates predetermined data to be transmitted into constant amplitude coded bi-orthogonal data, and demodulates the modulated constant amplitude coded bi-orthogonal data into original data and corrects errors in a wireless communication system using the code division multiple access. [0003] 2. Description of the Related Art [0004] As for schemes of modulating predetermined data to be transmitted in a communication system, there have been known a direct sequence/code division multiple access (DS/CDMA) scheme, a frequency hopping CDMA scheme, a complementary code keying (CCK) scheme, a multi-code (MC) CDMA scheme, a pulse width (PW) CDMA scheme, a multi phase (MP) CDMA scheme, and the like. [0005] Since the DS/CDMA scheme has a characteristic of constant amplitude and can employ a power amplifier with a simple configuration, its power consumption is relatively low. Further, it can ensure interference rejection capability by substantially performing spread spectrum modulation using Baker codes. However, its data transmission rate is low due to the frequency spread. Moreover, although it provides a variable transmission rate, there is a problem in that its effectiveness is low since the variable range is small. Thus, the DS/CDMA scheme has been mainly employed in IS (Interim Standard)—95. [0006] FH/CDMA-based communication systems have low power consumption and reduced production costs due to the use of simplified power amplifiers, and can ensure interference robustness through the frequency hopping. However, there are problems in that it cannot provide a high transmission rate and it is very limited in the capability of providing a variable transmission rate. [0007] The CCK scheme has been employed in IEEE 802.11b WLAN (Wireless Local Area Network). In the CCK scheme, there are advantages in that its power consumption is low due to the use of signals with a constant amplitude, production costs can be reduced due to the use of simplified power amplifiers, and it can provide a high transmission rate. However, there are problems in that it cannot ensure substantial interference rejection capability or provide a variable transmission rate. In addition, the CCK scheme can be considered as a kind of complex orthogonal modulation. Since code orthogonality for use in enhancing a characteristic of strong resistance against multipath fading may be damaged, there is a problem in that its performance rather degrades under the environment in which delay spread of the multipath fading is low. [0008] The MC/CDMA scheme is a method by which a plurality of orthogonal codes are assigned to a single user. It has been adopted as a standard of the third generation CDMA mobile communication system and described as a standard scheme of 3GPP (Third Generation Partnership Project) or 3GPP2 (Third Generation Partnership Project 2). The MC/CDMA scheme has been developed for providing a user with a high transmission rate and it is more likely to be continually used for a communication system that requires a high transmission rate. However, in a communication system using the MC/CDMA scheme, signals of the MC/CDMA are configured like passband PAM (Pulse Amplitude Modulation) signals when the signals of MD/CDMA are viewed in terms of a time axis. Since there are various amplitudes of transmitted signals so that the system requires a wide range of linear operation in a power amplifier used for a transmitter/receiver, it is difficult to manufacture the power amplifier and production costs thereof increase. If the constant amplitude characteristic can be obtained through a proper coding procedure in signal processing of a base band, passband signals also obtain a constant amplitude so that the production costs of the power amplifier can be greatly reduced and benefit can be obtained in view of power consumption. [0009] As a method of solving these problems incurred due to increase in the levels of modulated signals resulting from the use of multi codes involved with the increased number of channels of transmission data, the PW/CDMA scheme and the MP/CDMA scheme have been suggested. [0010] The PW/CDMA scheme limits output symbol levels of a digital adder to clip portions thereof exceeding a predetermined level value, converts only the values of the remaining levels into pulse widths, and then transmits the pulse widths, so that waveforms of signals always are in a binary form. Although the modulated signals are advantageously in the binary form, there is a disadvantage in that as the number of removed levels in the modulated signals increases, the bandwidth of the modulated signals increases in proportion to the number of the levels. [0011] The MP/CDMA scheme has been suggested as another method of obtaining signals with a constant amplitude. In the MP CDMA scheme, values exceeding a predetermined level value are clipped by a level limiter from symbols with various level values made according to the MC/CDMA scheme, the results obtained through the clipping are converted into phase values, and modulated signals with the converted phase values are amplified by and transmitted from a power amplifier. In other words, the PW/CDMA scheme is a scheme for limiting the output symbols according to the MC/CDMA scheme to a predetermined level and converting the remaining symbols into the pulse widths. The MP/CDMA scheme is a scheme for limiting the level and then converting the remaining symbols into the phases of carrier waves. [0012] The PW/CDMA scheme has an advantage in that the waveform can be simplified, but a problem in that as the number of remaining levels increases, the bandwidth of the modulated signals increase in proportion to the number of remaining levels. However, in the MP/CDMA scheme, the bandwidth becomes constant regardless of the number of levels. Further, in the MP/CDMA scheme, there is an advantage in that the system can be simplified since the level values of the signals are prevented from being increased by clipping portions exceeding a predetermined level value of the signals. [0013] However, the MP/CDMA scheme should use the same number of orthogonal codes as that of transmitted information channels since one orthogonal code is assigned to each channel of data transmitted. Thus, the number of orthogonal codes put to use increases as the number of data channel increases. Accordingly, in the procedure of limiting the levels of the multi-level signals, there is a problem in that the orthogonality of the orthogonal codes is damaged and thus mutual interference between the transmitted signals may happen. [0014] Therefore, an object of the present invention is to provide an apparatus for constant amplitude coded bi-orthogonal modulation, which performs the constant amplitude coded bi-orthogonal modulation for data in a communication system using the CDMA, thereby reducing power consumption of the system, manufacturing a power amplifier at an inexpensive cost, ensuring interference resilience and transmitting predetermined data at a high transmission rate and a variable transmission rate. [0015] Another object of the present invention is to provide an apparatus for constant amplitude coded bi-orthogonal demodulation, wherein errors of data subjected to the constant amplitude coded bi-orthogonal modulation are corrected by using additional data, which have been added for performing the constant amplitude coded bi-orthogonal modulation, as parity bits, and the performance of correcting errors of data bits of the system is improved. [0016] According to one aspect of the present invention for achieving the objects, there is provided an apparatus for constant amplitude coded bi-orthogonal modulation, comprising a serial to parallel converter for converting input serial data into a plurality of groups of signals each of which has a plurality of data bits, a signal having a plurality of data bits in one group selected among the plurality of groups, or a signal having one data bit and a plurality of data bits with a fixed value in the selected group, according to a data rate control signal; a constant amplitude encoder for generating parity bits by combining the plurality of data bits of each of the groups when the serial to parallel converter converts the serial data into the plurality of groups of signals each of which has the plurality of data bits; an orthogonal code generator for generating a plurality of orthogonal codes with different values; a plurality of bi-orthogonal modulation units for performing bi-orthogonal modulation by selecting one orthogonal code among the plurality of orthogonal codes according to the data bits of each of the groups converted by the serial to parallel converter and the parity bits generated by the constant amplitude encoder, and by adjusting the polarity; and a parallel summer for parallel summing up output signals from the plurality of bi-orthogonal modulators to generate constant amplitude bi-orthogonal modulated data. Each of the bi-orthogonal modulation units performs the bi-orthogonal modulation for the signal having one data bit (b0) and the plurality of data bits (b1, b2) with the fixed value in the selected group when the serial to parallel converter outputs the data bit (b0) and the plurality of data bits (b1, b2) with the fixed value. Each of the bi-orthogonal modulation units comprises an orthogonal modulator for selecting an orthogonal code (c0) generated by the orthogonal code generator according to the data bits (b1, b2); and a multiplier for multiplying the orthogonal code (c0) selected by the orthogonal modulator by the data bit (b0) to adjust the polarity and for generating the constant amplitude bi-orthogonal modulated data shown in Table 1 below.
[0017] Preferably, each of the bi-orthogonal modulation units performs the bi-orthogonal modulation for the signal having the plurality of data bits (b
[0018] According to another aspect of the present invention, there is provided an apparatus for constant amplitude coded bi-orthogonal demodulation, comprising: a bi-orthogonal demodulation unit for demodulating received constant amplitude bi-orthogonal modulated data, canceling parity bits and then generating serial data; an error detector for detecting the occurrence of an error while dividing the data demodulated in the bi-orthogonal demodulation unit into a plurality of groups of data and then outputting the serial data of the bi-orthogonal demodulator as demodulated data if an error does not occur; an error bit polarity converter for sequentially converting bit polarities of data of groups with errors if the error detector detects the errors and converting the data of groups with errors and the data of groups with no errors into the serial data; a constant amplitude coded bi-orthogonal modulator for performing the constant amplitude coded bi-orthogonal modulation for the output data of the error bit polarity converter; a distance comparator for comparing bit-by-bit distances between the received bi-orthogonal modulated data and the constant amplitude coded bi-orthogonal modulated data of the constant amplitude coded bi-orthogonal modulator; and a buffer for storing a number of serial data output from the error bit polarity converter and selectively outputting the corresponding serial data as demodulated data according to a control signal of the distance comparator. [0019] Preferably, the bi-orthogonal demodulation unit comprises a bi-orthogonal demodulator for demodulating the received bi-orthogonal modulated data; a parity bit canceller for canceling the parity bits from the output data of the bi-orthogonal demodulator; a plurality of switches for switching the data of the parity bit canceller according to the output signal of the error detector; and a parallel to serial converter for receiving the switched data from the plurality of switches if the error detector has not detected errors and converting the data into serial demodulated data. [0020] The error detector may comprise first to third parity checkers for receiving the plurality of groups of data output from the bi-orthogonal demodulator, checking the parity bits, determining the occurrence of errors and controlling the plurality of switches; and an OR gate for generating an error determining signal by performing an OR operation for output signals of the first to third parity checkers. [0021] The error bit polarity converter may comprise first to third bit polarity converters for receiving the data of the groups in which errors have occurred through the plurality of switches and converting their polarities; a plurality of OR gates for performing OR operations for output data of the first to third bit polarity converters and data with no error switched in the plurality of switches; and a parallel to serial converter for converting output data of the plurality of OR gates into serial data. [0022] The above and other objects, advantages and features of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which: [0023]FIG. 1 shows block diagrams of a transmitter and a receiver of a wireless communication system to which a constant amplitude coded bi-orthogonal modulator and demodulator of the present invention can be applied; [0024]FIG. 2 is a block diagram illustrating the detailed configuration of the constant amplitude coded bi-orthogonal modulator shown in FIG. 1; and [0025]FIG. 3 is a block diagram illustrating the detailed configuration of the constant amplitude coded bi-orthogonal demodulator shown in FIG. 1. [0026] Hereinafter, a constant amplitude coded bi-orthogonal modulator and demodulator of the present invention will be described in detail with reference to the accompanying drawings. [0027]FIG. 1 shows block diagrams illustrating configurations of a transmitter and a receiver of a communication system to which the modulator and demodulator of the present invention are applied. Here, reference numeral [0028] The transmitter [0029] In the baseband unit [0030] Here, the constant K is the required channel bandwidth in a pass band and is obtained as follows: [0031] where A is the required minimum bandwidth in the pass band and a is the roll-off factor of a filter. [0032] The data input into the signal splitter [0033] The inphase and quadrature components split in the signal splitter [0034] Data output from the pseudo-noise code scrambler [0035] Further, in the receiver [0036] Output signals of the filter [0037] The signals descrambled in the pseudo-noise code descramblers [0038] In a case where biphase shift keying (BPSK) is used in the transmitter and receiver of such a communication system, the transmitter [0039] The foregoing description means that the maximum spectral efficiency is 9/8. That is, the present invention is very efficient and a large amount of data can be transmitted. The various transmission rates can be provided in accordance with the environment of the transmission channel, and it is possible to maintain interference robustness by performing reliable constant amplitude coded bi-orthogonal modulation and demodulation in accordance with the transmission rate. [0040] In addition, receivers with the same configuration can be used for the various transmission rates, and linearity requirements for linear operation ranges of the power amplifier [0041]FIG. 2 is a block diagram illustrating the detailed configuration of the constant amplitude coded bi-orthogonal modulator [0042] Each of the plurality of bi-orthogonal modulation units [0043] The operation of the constant amplitude coded bi-orthogonal modulator of the present invention constructed as above will be described according to the provided data rates. [0044] 1. In Case of Providing the Data Rates of K/16 Mbps and 2K/16 Mbps [0045] In case of providing the data rate of K/16 Mbps for BPSK and 2K/16 Mbps for QPSK, a parallel sequence of data bits is provided by only one bit with respect to inphase and quadrature phase axes. That is, the serial to parallel converter [0046] The orthogonal modulator [0047] That is, in case of providing the data rates of K/16 Mbps and 2K/16 Mbps, only the bi-orthogonal modulation unit
[0048] 2. In Case of Providing Data Rates of 3K/16 Mbps and 6K/16 Mbps [0049] In case of providing the data rate of 3K/16 Mbps for BPSK and 6K/16 Mbps for QPSK, a parallel sequence of data bits is transmitted by three bits with respect to the inphase and quadrature phase axes. That is, the serial to parallel converter [0050] The data bits (b [0051] Even in case of providing the data rate of 3K/16 Mbps for BPSK and 6K/16 Mbps for QPSK, only the bi-orthogonal modulation unit
[0052] 3. In Case of Providing Data Rates of 9K/16 Mbps and 18K/16 Mbps [0053] In case of providing the data rate of 9K/16 Mbps for BPSK and 18K/16 Mbps for QPSK, a parallel sequence of data bits is transmitted by nine bits with respect to the inphase and quadrature phase axes. That is, the serial to parallel converter [0054] The data bits (b [0055] When the parallel summer [0056] Therefore, in the present invention, in order to cause the amplitude of the bi-orthogonal modulated data output from the parallel summer {overscore (b _{3})}{circle over (+)}{overscore (b (2) _{6})} [0057] where {circle over (+)} represents XOR. [0058] The generated parity bits (r [0059] Therefore, if the spread ratio is 16, the constant amplitude bi-orthogonal modulated data are obtained. The overall spectrum efficiencies in cases of using BPSK and QPSK are 9/16 and 18/16, respectively. Thus, the data rates of 9K/16 Mbps and 18K/16 Mbps can be obtained. [0060]FIG. 3 is a block diagram illustrating the configuration of the constant amplitude coded bi-orthogonal demodulator [0061] The bi-orthogonal demodulation unit [0062] The error detector [0063] The error bit polarity converter [0064] In the demodulator of the present invention constructed as above, the received constant amplitude bi-orthogonal modulated data are demodulated in the bi-orthogonal demodulator [0065] In addition, the demodulated data (b [0066] Here, assuming that all of the first to third parity checkers [0067] Then, the demodulated data (b [0068] In addition, if any one of the first to third parity checkers [0069] Here, assuming that the first parity checker [0070] In addition, the demodulated data (b [0071] Then, the parallel to serial converter [0072] Here, the constant amplitude coded bi-orthogonal modulator [0073] Then, the distance comparator [0074] As described above, the modulator according to the present invention performs the constant amplitude bi-orthogonal modulation for predetermined data to be transmitted. Since the data have the constant amplitude, when they are applied to a communication system, power consumption of the communication system can be reduced. Since the linear operation range of the power amplifier can be narrowed, the power amplifier can be manufactured at an inexpensive cost. Further, interference rejection capability ( interference robustness) can be ensured and the predetermined data can be transmitted at a high transmission rate and a variable transmission rate.[0075] In addition, the demodulator of the present invention performs demodulation while correcting errors by using the parity bits added when the data are modulated, so that the modulated data can be correctly demodulated without the occurrence of errors. [0076] While the present invention has been illustrated and described in connection with the preferred embodiments, it will be readily understood by those skilled in the art that various modifications and changes can be made thereto without departing from the sprit and scope of the present invention defined by the appended claims. Patent Citations
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